Antistatic receiving system



JHM 24, 1941- w. E. zuccARELLo ANTISTTIC RECEIVING SYSTEM Filed Nov. e, 1939 Patented June 24, 1941 UTED ST S ATE @FEE ANTISTPLTC RECEIVING SYSTEM Application November (i, 1939, Serial No. 302,959

(ci. 25o-co) l2 Claims.

The present invention relates to radio systems designed to prevent interference from extraneous electrical disturbances, such as static from natural or artificial sources, The invention represents an improvement over the system which is described and claimed in my co-pending application Serial No. 240,547, filed November 15, 1938, and entitled Antistatic receiving system and which has matured into Patent No. 2,200,- 613.

In the past, many attempts have been made to eliminate static interference from radio receiving systems, but in general these attempts have culminated in failure due, in a large part, to the fact that the exact character of static impulses has not been sufliciently taken into account, nor has the deleterious elect of these impulses on the modulated carrier been given suflicient consideration. In order that the present improvement over existing systems will be thoroughly understood, it is desirable to set forth certain fundamental assumptions, the correctness ci which has been fully ascertained by elaborate experiments.

The rst oi these assumptions is that there is no static that is audible which decreases the carrier, i. e., a static impulse cannot cause audible decrease of the carrier. Static is not tunable within practical limits, because it is highly damped. The static shock-excites the tank coils of the coupled circuits, causing continuous waves to be set up therein regardless of the frequency to which the coil is tuned. Individual discharges, such as lightning, last 1,430,000 of a second; therefore, to increase the carrier wave of a given strength forv an audible period, the impulse would have to heterodyne against the carrier, beginning as an inaudible heterodyne note, proceeding to an audible note with a simultaneous decrease in power to an inaudible note again, all within 130,000 of a second period. The first powerful static impulse causes the currents in the tank coil to oscillate in direct proportion to the strength of the static which may be many times greater than the carrier, causing an audible current to build up of a duration and amplitude sufcient to attuate a speaker diaphragm which vibrates usually long after the initial build-up has ceased. Any swing of the tank coil current that is less than the carrier current is immediately brought back to carrier strength by the next carrier oscillation.

Static impulses which are in phase with the carrier do not decrease the voltage, whereas static impulses which are out of phase tend to reduce the carrier for one cycle, after which the next cycle carrier brings the tank coil current back to the original power. In other words, in order to receive static, the latter must be highly damped or it would be tunable. To be highly damped, the static must be of short duration and if it is not highly damped, the static causes little or no interference.

rThe second proven assumption is that, within a given practicable Wave band, coupling coils have nearly the same angle of decrement which is evidenced by the same static noise at either end of the band. Decrement depends upon resistance, coupling and radiation, more than upon capacity, in the commercial tank or coupling coils; the iirst three are practically the same regardless of capacity. Shorter frequency tuning radiates more than longer frequencies, but not enough to make any great change in the angle of decrement. Therefore, for a given practical band of frequencies, the decrement is practically the same and only the amplitude need be considered in balancing.

The third assumption, on which the present invention is based, is that only direct current can successfully be balanced by grid action or otherwise, and the frequency of the source of interference does not necessarily control the audible note. Only the angle of decrement oi the static source and the ampliication of the receiver determine the static note or noise.

The final principle on which the present invention is based is that radio telephony is accomplished commercially by increasing and decreasing the carrier strength (above and below a mean), but static energy is always an increase from Zero to maximum and back to zero, never above and below a xed mean strength. Therefore, to balance such conditions, only a direct current can be successfully used. Any circuits purporting to use transformers (audio) or condensers, which tend to create or convert to alternating current are irnpracticable. Any circuits which purport to use push-pull transformers or any like arrangement of balancing will not balance, due to the above conditions and the action of the lines of force in the transformer.v Any circuit which uses 'the automatic volume control (A. V. C.) feed back of the ordinary ,type to the grids of the radio frequency coils merely reduces the strength of the signal carrier during a static impulse. If this impulse is sufciently rapid, as in the case of atmospheric disturbances, the automatic volume control circuit may cut off the carrier entirely. Hence, there are no means of eliminating the static that lls in the carrier modulations. Any circuit to lter static can only do so on the frequency of the filter limits. Any prior circuit that limits the maximum increase over carrier strength distorts the signal, as no method is used to take out carrier impulses when the carrier is modulated.

Furthermore, any method that purports to balance by the use of two separate receiving channels and does not shape the received power static to the same characteristics as that static which is impressed on the signal cannot balance out static on any signal, but can only limit the power of the static. The stronger the static, the less the balance and the greater the noise, as the power cf the static without the carrier will cut into the signal strength, causing as much noise on strong signals or more than static itself on the signal. On weak signals, the oscillograph shows the ear as being deceived and, upon amplification, noise would again be heard under these conditions, because no attempt is made to cancel the static that is being received during the modulation of the carrier to zero or near zero.

In my co-pending application referred to hereinbefore, there is disclosed and claimed a system which relies for its effectivness on the four fundamentals which have been discussed at length hereinbefore. This system employs two parallel receiving circuits, one of which is adapted to respond to a combined modulated carrier and audible static impulses, the other being adapted to respond to only audible static impulses. There is provided a mixer or balancing tube in which the static impulses are caused to oppose one another and in this manner, canceled. The adaption of the two parallel receiving circuits to the different functions described immediately above is brought about by an automatic volume control or feed back system, which has its origin in the mixer or balancing tube. Thus, the latter is called upon to exercise two functions, namely, to bring about a difference in the amplifying properties of each of the two parallel receiving circuits so as to make them respond differently to the static and the combined modulated carrier-static impulses and in addition, the tube serves to cause the static impulses to oppose one another and thus be eliminated from the audio receiving portion of the system.

Accordingly, the primary object of the present invention is to simplify the circuits and apparatus employed in eliminating static from any source whatsoever.

A more particular object is to provide a radio system which Will receive the static impulses of an audible character together with a modulated carrier, but thereafter precludes the static from reaching the telephone receiver. A still further object is to cause the audible static impulses to cancel one another within the system.

Finally, the more specic object is to improve on the system disclosed and claimed in my copending application referred to hereinbefore, in that the function of procuring a different amplification in the two receiving circuits, by which the static is effectively eliminated from the system, is separated from the mixer or balancing tube. Consequently, the latter can be so designated and operated to perform the sole function of balancing out the deleterious static impulses in the most efficient manner Without having to perform the selective amplification function.

These objects are attained in brief by providing a tube in addition to the mixer or balancing tube, which additional tube is so related to the circuits as effectively to control the amplification properties of the two parallel receiving circuits. This tube is preferably of the same type as the mixer or balancing tube, and has elements connected in parallel to the corresponding elements of the balancing tube, but is operated at a point on its characteristic curve, such as to perform the selective amplification function referred to hereinbefore most effectively.

Other objects and features will be apparent as the specification is perused in connection with the accompanying drawing. This drawing shows a typical electrical system with the tubes diagrammatically illustrated for carrying my invention into effect.

Referring to the drawing, numeral l designates an antenna to ground system. Coupled to this antenna through the transformers 2, 3, there are a pair of parallelly connected radio receiving circuits which are designated circuit A and circuit B, respectively. As will be explained hereinafter, each of these circuits constitutes a single stage of radio frequency amplification, a heterodyne-oscillator stage, one or more stages of intermediate frequency amplification, and finally a detector stage. These circuits are identical in construction and arrangement, for reasons which will be stated hereinafter, the only difference being in the nature of the feed-back circuit or automatic volume control connection made to the various stages. Consequently, a description of only one circuit is necessary, since the other is a duplicate except for the details mentioned.

The radio frequency stage is preferably constituted of a pentode f-i, in which the control grid 5 is connected to the tank coil 2 through a Variable condenser 6 and a small fixed condenser 7. @ne terminal of this condenser is grounded at 8. The cathode 9 which is indirectly heated by the filament it is connected directly to the suppresser grid Il. The screen grid l2 is connected to a source of positive voltage indicated by the arrow line which may lead to a double wave rectifier described hereinafter. This screen grid surrounds a well-known space charge grid I3 connected to a positively charged terminal l5.

' The anode i4 is connected through the primary winding of a coil i6 to another terminal Il of positive potential.

The condensers leading to the grid I2 and the anode M are shunted by a pair of fixed condensers i8 to ground so as to prevent radio frequency currents from passing through the terminals I3, il into the rectifier. The secondary winding of the transformer EB is shunted across a variable condenser i9 and a small fixed condenser Ell to ground at 2l to constitute a tuned circuit for the input of the oscillator-demodulating device 22. This device is constituted of a combined triode and tetrode of the ordinary construction. The triode is made up of the cathode 23, control grid 2li and the grid-like anode 25, all of which cooperate to produce oscillations through the feedback connection 26, which oscillations are impressed or combined with the impulses applied to the control grid 27 of the frequency mixing portion of the tube. The control grid 2l is preferably enclosed within a screen grid 28 for well-known purposes and cooperates with the cathode 23 and the anode 29 to amplify and mix the received electrical impulses with the oscillations produced in the triode portion of the tube,

the cathode 23 being preferably of the indirectly heated type as indicated. The immediately associated circuits by which these results are obtained will now be described.

The cathode 23 is connected through the usual grid leak resisto-r 30 and the condenser 3l to ground at 32 so as to provide the p-roper bias to the grids of the heterodyne oscillator. The grid 24 is additionally biased by means of a grid leak resistor 33 and a condenser 311. The condenser 34 is connected through the primary of the feedback coupling 26 through a variable condenser 35 and a xed condenser 3B to ground at 3l. The grid-like anode 25 of the oscillator is connected through the secondary of the coupling 26 to ground through a condenser 33. A connection from this circuit is also made to a terminal of positive potential indicated at 39 through a resistor 4D. The screen grid 28 is connected through condenser 4I to a terminal 42 of positive potential. The anode 29 is connected through a tuned circuit consisting of a variable condenser 43 and a transformer primary 44 to a radio frequency choke 45 and thence to a terminal 46 of positive potential. Radio frequency currents are prevented from reaching the terminals 42 and 46 by means of radio frequency by-pass condensers 4l which are connected to ground at 48.

The circuit which has been described up to this point constitutes one stage for radio frequency and a combined oscillator-demodulating stage Z2, the frequency of which can be adjusted by the variable condenser 35 to beat with the incoming frequency impulses applied to the grid 2l and to pass on through the transformer 44 the difference frequency which is considerably lower than fthe radio frequency and is thereafter amplified by the intermediate frequency amplifiers to be described presently. The first two stages of the receiving system are of standard type so that no information need be given as to the size and adjustments of the various condensers, resistors, coils, etc. other than to point out that the input circuits of these stages are both tuned to the received carrier, and the coupling circuit 43, :ist is tuned to the difference frequency obtained by the heitercdyning action of the tube 22,

The intermediate frequency amplification stage is exemplified by the pentode tube lit. This tube contains an indirectly heated cathode El, ia control grid 52, a, screen grid 53, a suppressor grid 54 and an anode 55. The biasing potential for some of these grids is obtained by a resistor-condenser network t to ground. The suppressor grid is connected directly back to the cathode. The control grid 52 is connected through a condensertransformer coupling circuit indicated generally at 5l to the output circuit of the tube 22. The.

screen grid 53 is connected to a source of positive potential 5S. The anode is energized by current obtained from the terminal 5S through the primary of the coupling coil til. Radio frcquency currents are by-passed around the sources of direct current potential vby means of condensers 49 connected to ground.

Als stated hereinbefore, the purpose of the tube 5B is to amplify the difference frequencies obtained from the heterodyne tube 23 `and to pass. these currents on to the detector Si. This detector may take any suitable form, but, as illustrated, operates on the dio-detection principle. The diode has an indirectly heated cathode (i2, a grid-like element 63 which serves the function of the rectifier anode and an element 64. The secondary of the coupling coil 6D is grounded through a fixed condenser 65 `and is provided with a variable condenser B6 for tuning purposes. The tuned circuit 60, 66 is made responsive to the intermediate frequency impulses and, by means of a connection tl, impresses these impulses on ithe element 63. The electrode t4, which is illustrated as an anode, but which simply constitutes the` cathode of the rectifier, is connected directly to the thermionic. cathode 62. The element t4 is connected through a condenser-resistor network 58 and a radio frequency choke E9 to the upper plate of the condenser 55. The electrode 64 is connected through this network to a tap W5 on the negative side of the resistor l2. This resistor is. connected across fthe output circuit of a typical full-wave rectifier 'i3 which need not be described in detail. Condensers 'i4 are provided for grounding the radio frequency currents which might find their Way into the rectifying circuit. Radio frequency choke coil 'i5 is provided for a similar purpose. As will be noted, an intermediate point on the resistor 12 of the rectifying circuit is grounded at 'it so that all potentials taken off from points to the left of ground represent the negative potentials, and those to the right represent positive potentials.

The purpose of the tube Gi is to rectify the incoming waves and, in particular, to eliminate the carrier so that the potential drop across the network 68 is devoid of carrier, but contains` all of the other components including the signal which has been passed through the coupling circuits of the amplifying and heterodyning stages. A connection 'iii is taloen from a point between the electrode t4 and the resistor of the network t8 to the control grid of a mixer or balancing tube, which will be described presently.

As stated hereinbefore, the circuit B is similar to circuit A, except for a few details. which will be referred to specifically. It is, therefore, unnecessary to duplicate the description of these circuits and, for convenience in referring to the various elements of the two circuits, the elements of circuit B have been given the same reference character as the corresponding element of circuit A, except that a small b has been` inserted after the reference character.

The mixer or balancing tube 'il includes an indirectly heated cathode l', a control grid lil, another control grid 89 which is shielded from. the control grid T9 by a scr-een grid iii, a suppressor grid 82 and an anode 33. The output currents from the detector 3| of circuit A are conducted to the grid 'i9 of the mixer or balancing tube 1l. On the other hand, the output currents of the detector @Ib of the circuit B are taken by the conductor 84 to the control grid liti of the tube ll. t will be noted that the conductor lll is connected to a point on the upper side of the resistor-condenser network 5B, whereas. the conductor 3ft is connected to the lower `side of resistor-condenser network 68h. Consequently,

the output currents of the detectors El and till)l are impressed on `their grids in opposition to one another in the tube ll. The cathode 'i3 and the suppressor grid 82 of .the tube ll are charged negatively with respect to ground due to the position of the terminal 35 on the resistor l2. The screen grid 3i of the tube 'l1 is likewise charged negativeiy at the .terminal 85. The anode 83 is connected through a conductor 3l, a fixed condenser 83 and a iixed resistor 39 to the ground terminal on the resistor l2. The purpose of the resistor 89 and this ground connection will be described hereinafter.

A resistor 8| is connected between the condenser 38 and ground, from which a variable tap 92 is taken to the control grid 93 oi' an audio frequency amplifier fill. This ampliiier includes an indirectly heated cathode 55 connected through a grid biasing network Gtia to ground. The usual screen grid and suppressor' grids. are provided, also an anode f: which is connected `through an .audio frequency coupling 9i to any audio ampliiier and receiver arrangement which have been merely indicated on the drawing, since their construction is well known.

As stated hereinbefore, the present invention depends for its eiectiveness in removing or cancelling static upon the feature of balancing out that part of the static impulses which have been found to be most deleterious by way of objec tionable noise in the telephone receiver. Experiments have shown that that part of the static impulse, which is of greater intensity than the carrier or which in any other manner overrides the carrier, is the part which is most objectionable. For that reason, I propose to so adjust the circuits A and B that one of the circuits, for example circuit A, will be tuned to receive the combined signal-modulated carrier and static impulses, whereas the other circuit, for example circuit B, will be so adjusted as to receive only the static impulses which override the carrier. The difference in adjustment of the circuits which are otherwise identical, except for the detector stage, is brought about by energy feed-back circuits of different character. Thus, in circuit A, the energy feed-back circuit is indicated at 98 and is taken through a resistor 99 and a condenser |95 to ground, the said circuit having connections to each of the rst three stages of circuit A.

Fixed resistors is! are connected between cer-v tain grid circuits of the tubes d and 22 to the conductor 98 so as to prevent inner-tube oscillation. A direct connection is made between the input circuit of the tube 5S and the conductor S8 to a point between the resistor iid and the conductor |00.

On the other hand, the feed-back connection |2 in circuit B is passed through a radio frequency choke |83 to the various stages. It will be noted that each of these feed-back connections originate at a point marked l2@ on the drawing to which plate current is fed as will be explained hereinafter. inasmuch as each of these feed-back connections originates from the same point, the same components ow through these circuits except such as are prevented or otherwise attenuated by the resistor B-condenser Iii network in circuit A and the radio frequency choke G3 in circuit B.

In my co-pending application Serial No. 240,- 547, this current was taken from the plate circuit of the mixer or balancing tube but in accordance with the present invention, better results are obtainable in more eiiectvely eliminating the static by employing a tube separate from the mixer or balancing tube for providing the feed-back current. Thus, in the improved sysu tem the function of balancing the static in circuit A against the static in circuit B is separated from the function of supplying the feed-back energy which controls the amplification factors of the respective circuits. This additional tube is illustrated on the drawing at iil'i, which preferably is of the same type as the mixer or balancing tube '11. Thus, tube I'l contains six electrodes, the indirectly heated electrode being indicated at |88, the plate at It, the screen grid at H0, the suppressor grid at and the dual control grids at H2 and H3, respectively. The cathode |08 is connected through a wire H4 to a tap H5 on the resistor 12. The control grid H2 is connected through a conductor H6 to the iirst control grid of the tube il. and the other control grid ||3 is connected through a wire H'l to the control grid of the tube 7l. The control grids H2, H3 of tube |01 are thus connected in parallel to the corresponding grids of the tube TI. The screen grid Htl is grounded at H8. The suppressor grid is connected back to the cathode. The plate It!) is connected through a conductor H9 to the junction point |20 of the two feed-back or automatic Volume control circuits 98 and Iii?. The plate is also connected to ground at |2| through a fixed resistor |22.

It will also be noted that in addition to the feed-back |82 in circuit B, there is an audio frequency feed-back |23 connecting the plate 83 of the balancing tube 'El with the grid |3b of the first radio frequency stage. A condenser |24 is connected in this feed-back circuit.

Operation of the circuit The grid 'I9 of the balancing tube receives rom circuit A combined signal and static impulses (the carrier has already been eliminated in the detector 6|) and the grid 8i! receives only static impulses greater than carrier intensity from circuit B. The effect of static 0n grid 80 is opposite to the eiTect of the static component on grid i9, because as one grid is driven negative, the other is driven positive with respect to the cathode. This is due to the fact that the conductor i6 is connected to the opposite side of the network 68 from the side to which conductor Sli is connected to its network 63h.

The audio frequency feed-back circuit |23 serves to modify the shape of the static impulses which flow through circuit B to conform with that of the static impulses in circuit A. It is apparent that any difference in the shape of the static impulses flowing through circuits A, B, is immediately reflected in the output circuit of the balancing tube and corrective impulses are transmitted through the circuit |23 to the radio frequency amplifier lib. Thus, a cancellation or balancing out eiect of static impulses of greater intensity than the carrier takes place in the tube ll. In order to prevent inter-electrode capacity errors, the grids i9 and 8d are shielded from one another by the screen grids 3|.

The grid 19 of the tube i? is preferably biased by means of the tap so that the tube will cut oi when there is no signal. It will be noted that the plate 83 is connected to ground through the resistor 69 so that, when no signal current is passing through the tube, the plate is maintained at zero potential. On the other hand, when signal currents are flowing, the plate is maintained at negative potential due to the drop in the resistor. Thus, the tube 'i7 is maintained in a highly sensitive condition between signals.

The current which is fed to the input circuit of the audio frequency amplifier Elli, through the tap 92, is devoid of static, at least of that static which is of greater intensity than the carrier and which normally is most objectionable in the telephone receiver. The static which is of less intensity than the carrier is not so harmful from the auditory standpoint, since it does not mask out the signals or speech to any great extent and readily permits discrimination at the receiver.

By providing two parallel circuits, stages of which are substantially identical, assures that the same electrical actions are performed by the tubes and their various coupling circuits including the tank coils on the static in both circuits. Any difference in the wave form between the static components in circuits A and B is compensated by the audio frequency feed-back circuit |23. Consequently, the balancing tube receives two static impulses of exactly the same wave shape, which can cancel one another. It will benoted that the cancellation of the static impulses is performed solely by the use of direct currents in the balancing tube and, therefore, entails the only practical way in dealing with static as is fully discussed under the fourth assumption set forth at the beginning of the specification.

In order that the grids 'i9 and til' will have the same effect, but in the opposite sense, on the electron stream in the balancing tube, notwithstanding their difference in position with respect to the cathode, the bias on these respective grids is maintained at dilierent values and controlled by the tap 'H which is connected through the resistor of the network 68h to the grid 8i).

Now, supposing that notwithstanding the fact that proper potential adjustments have been made in the balancing tube to give a theoretically complete balance or cancellation of the two opposite static impulseaiit was found that objectionable static still could be heard in the receiver. The function of the tube lill comes into play at this point. The lack of balance between the two static impulses is registered in this tube because the grids H2, H3 are connected in parallel to the grids lil, 863 of the balancing tube. The difference in the charges on the two grids H2, H3 will cause either an increase or decrease of plate current to ow through the tube lill, depending on the direction which the lack of balance takes, Thus, a negative charge, for example, on grid H2 may increase at a faster rate than a positive charge on grid H3 in which case the plate current is decreased and under opposite conditions, the plate current will increase. This change in plate current through the tube till affects the feed back circuits 9B, HB2 in a different manner due to the different attenuating elements in these two circuits. It is apparent that the nature and adjustment of these elements can be controlled in such a way that the difference in the character of the 'feed back current or voltage will discriminate between the circuits A and B as to their respective amplifying properties.

Using the elements as illustrated I have found that it is feasible to reduce the amplifying property of circuit B, for example, to such an extent that it will respond to antenna energy only above a predetermined amount, at the same time leaving circuit A with its full or other desired amplification. 'Ihis circuit A will be permitted freely to respond to modulated carrier and static, whereas circuit B will be biased to such an extent that it will respond only to static above a predetermined intensity level, for example, above carrier strength. Any change in the plate current flowing through the tube lli'l as a result of unbalanced static will therefore cause a change in the amplifying properties of the circuits A and B to such an extent that the static impulses transmitted through these respective circuits, on arriving at the control grids 'i9 and 80 of the balancing tube will completely cancel one another. Thus, no deleterious static effect is carried to the audio amplifying system generically indicated at 94.

Whereas in my `co-pending application Serial No. 240,547, the static balancing out eifect and the function of feeding back energy to the two amplifying circuits were performed in the same tube, namely the so-called balancing tube, I find that more effective results are obtainable by providing separate tubes for these functions. Thus the tube ll may be properly biased through the the tap to perform the static balancing out or cancellation effect in an optimum degree and likewise the tube IEN can be suitably biased at the tap H5 to perform its own feed back function. In general, the iiXed potential on the elements of tube I nl are such that the tube operators on the knee portion of its grid voltageplate current characteristic, at which position a wider plate voltage swing is obtained for a given grid voltage variation. Consequently, any small differential change of the potential applied to the grids H2, H3 produces an instantaneous and substantial change in the feed-back current or voltage supplied to the circuits 93 and m2.

Modifications of the system which has been shown and described will readily occur to those skilled in the art. For example, any number of high and intermediate radio frequency stages may be employed, and other well-known forms of receiving circuits used to advantage, provided these circuits lend themselves to automatic volume control feed-back which will selectively control the amplifying properties of the two circuits, and in that manner cause one of the circuits to respond to the deleterious impulses which are eventually cancelled out in the balancing tube.

Consequently, it will be understood that I desire to comprehend within my invention such modifications as come within the scope of the claims and the invention.

Having thus fully described my invention, what I claim as new and desire to secure by Letters Patent is:

1. A static eliminating system comprising two radio receiving circuits, means including one of said circuits for receiving combined signal-modulated carrier and static impulses, means including the other of said circuits for receiving only those static impulses which are of greater strength than the carrier, means for differentially balancing the output currents of one circuit against the output currents of the other circuit, and means for equalizing the amplitudes of the static impulses of both circuits whereby the static impulses of greater strength than the carrier are completely removed in the balancing means, and means for amplifying the differential currents.

2. A static eliminating system comprising two radio receiving circuits, means for tuning one of said circuits to respond to the combined signalmodulated carrier and static impulses, means for adjusting the other circuit to respond only to the static components of greater strength than the carrier, a balancing tube for combining the output currents of the circuits in a differential manner, and an additional tube for equalizing the amplitudes of the static components which have greater strength than the carrier, whereby the combined balancing and equalizing tubes serve to remove static impulses of greater strength than the carrier from the signal.

3. A static .elimination system comprising two radio receiving circuits, one of which receives the combined signal-carrier and static impulses and the other receives only the static impulses which override the carrier, means for cancelling the deleterious static components of the currents flowing through the responsive circuits, said means including a pair of tubes, one of which is biased eiectively to balance the static impulses of greater intensity than the carrier in said circuits against one another and the other is biased effectively to control said circuits in such manner as to equalize the static impulses received by said circuits and of greater intensity than the carrier whereby complete cancellation of these impulses takes place within the system.

4. A static eliminating system comprising two radio receiving circuits, one of which receives the combined signal-carrier and static impulses and the other receives only the static impulses which override the carrier, means for cancelling the deleterious static component of the currents flowing through the respective circuits, said means including a pair of tubes, one of which is biased .effectively to balance the static impulses of greater intensity than the carrier in said circuits against one another, and the other is biased effectively to change the differential amplification of the receiving circuits in such manner as to equalize the static impulses of greater intensity than the carrier reaching the balancing tube and complete cancellation of these impulses takes place within the .sytsem.

5. A static eliminating system comprising two parallel heterodyne radio receiving circuits each including a detector, a balancing tube for differentially combining the output currents of said circuits, an additional tube which responds to thestatic components of said output currents, means including automatic volume control circuits connected between the output circuit of said additional tube and said receiving circuits for causing one of the receiving circuits to respond to combined signal-modulated carrier and static impulses and to cause the other of said receiving circuits to respond to static impulses which override the carrier whereby the output circuits of said balancing tube contains no static of greater intensity than the carrier, and means for translating the output current of the balancing tube into sound undulations.

6. A static eliminating system comprising two parallel heterodyne radio receiving circuits each including a detector, a tube for balancing predetermined components of the output current of one of said circuits against similar components of the output current of the other of said circuits, means including an additional tube for feeding back energy to one of the receiving circuits, said energy being of such character as to permit its receiving circuit to respond to the combined signal-modulated carrier and the static impulses, means including said additional tube for feeding back energy to the other of said receiving circuits, said energy being of such character as to permit its receiving circuit to respond only to static impulses which override the carrier whereby the audible static impulses are balanced out in the balancing tube, leaving only the signal component, and means for translating the signal component into audible undulations.

'7. A static eliminating system comprising two radio receiving circuits, means for cancelling the static component of the currents owing through the respective circuits, said means including a pair of tubes, one of which is biased to oppose the effects of the static impulses in said circuits against one another, and the other tube is biased eiectively to feed back energy to the circuits in proportion to the preponderation of static in one circuit over the static in the other circuit whereby complete cancellation of the static impulses takes place Within the system.

8. A static eliminating system comprising two radio receiving circuits, a balancing tube for differentially combining the output currents of said circuits, said tube including a pair of control grids to which said receiving circuits are respectively connected, means including a thermionic device for causing one of the receiving circuits to respond to combined signalmodulated and static impulses and to cause the other of said receiving circuits to respond to static impulses which override the carrier, said thermionic device including a pair of control grids connected respectively to each of the control grids of the balancing tube, and means for translating the output current of the balancing tube into sound undulations.

9. A static eliminating system comprising two parallel radio receiving circuits, each including a plurality of tube elements of similar number and character, means for adjusting one of said circuits to receive combined signal-modulated carrier and static impulses, means for adjusting the other of said circuits to receive only the static impulses which override the carrier, means including an electron device common to both circuits for maintaining both of said adjustments, and means for balancing the audible static currents in one circuit against the audible static currents in the other circuit whereby the deleterious static impulses are removed from the signal, and means for translating the signal impulses into sound undulations.

l0. A static eliminating system comprising two radio receiving circuits, means for cancelling the static component of the currents flowing through the respective circuits, said means including a balancing tube and a feed back tube, each containing a plurality of grids, the grids of the balancing tube being biased to cut oi the anode current of the tube when no signal passes through the radio receiving circuits, the bias on the grids of the feed back tube being such as to cause the tube to operate at the knee portion of its grid voltage-plate current characteristic curve, said tubes operating collectively to equalize the static components in the respective receiving circuits and to balance out these components, and means for translating the output signal current of said receiving circuits into sound undulations.

11. A static eliminating system comprising two parallel radio receiving circuits, each including a plurality of tube elements of similar number and character, a ldetector tube in each of said circuits, means for balancing the static output currents from one detector tube against the static output currents from the other detector tube, said balancing means comprising a balancing tube having an anode and a plurality of grids, said static output currents being applied in a dilerential manner to said grids, one of said grids being biased to cut off the anode current in the balancing tube when no signal passes through the detector stage, an additional thermionic device including a plurality of grids vand an anode, said grids being connected respectively to the grids of the balancing tube, an energy feed back connection from the anode of said thermionic device to each of said receiving circuits to adjust one of said circuits to respond to the combining signal-modulated carrier impulses and to adjust the other of said circuits to respond only to static impulses which override the carrier, Whereby the static impulses applied to one of the grids of the balancing tube are constituted of signals mixed with static and the impulses applied to the other grid of the balancing tube are constituted solely of static so that the differential effect of these grids is to balance out static above a predetermined intensity, leaving only the signal currents and static below said predetermined intensity, and means for translating the signal currents into sound undulations.

l2. A static eliminating system comprising two parallel radio receiving circuits, each including a plurality of tube elements of similar number and character, a detector tube in each. of said circuits, means for balancing the static output currents from one detector tube against the static output currents from the other detector tube, said balancing means comprising a balancing tube having an anode and a plurality of grids, said static output currents being applied in a differential manner to said grids, one of said grids being biased to cut off the anode current in the balancing tube when nov signal passes through the detector stage, the anode of the balancing tube being maintained at zero potential when no signal is passing through the detector tube by automatically being biased negatively when signal impulses are passing through the detector stage, an additional thermionic device including a plurality of grids and an anode, said grids being connected respectively to the grids of the balancing tube, an energy feed back connection from the anode of said thermionic device to each of said receiving circuits to adjust one of said circuits to respond to the combining signal-modulated carrier impulses and to adjust the other of said circuits to respond only to static impulses which override the carrier, whereby the static impulses applied to one of the grids of the balancing tube are constituted of signals mixed with static and the impulses applied to .the other grid of the balancing tube are constituted solely of static so that the differential effect of these grids is to balance out static above a predetermined intensity, leaving only the signal currents and static below said predetermined intensity, and means for translating the signal currents into sound undulations.

WILLIAM E. ZUCCARELLO. 

